Abstract: The microstructure evolution of AZ31 magnesium alloy sheet during the room temperature bending and straightening process and its effect on the mechanical properties were studied. The results show that the prefabrication of tensile twins by the room temperature bending and straightening process not only contributes to the plastic deformation of the magnesium alloy, but also has a positive effect on the improvement of the strength of the material. After bending and straightening at room temperature, the sheet produces tensile twins, and it leads to grain refinement and dislocation strengthening caused by the energy accumulation of dislocations at the grain boundaries, which improves the tensile strength of the magnesium alloy sheet. At the same time, the prefabricated tensile twins weaken the basal texture and can activate more types of slip systems, leading to an increase in the elongation of the sheet after bending and straightening at room temperature.